eX FPGA Architecture and Characteristics
1-6
Revision 10
The eX family supports mixed-voltage operation and is designed to tolerate 5.0 V inputs in each case.
Hot-Swapping
eX I/Os are configured to be hot-swappable. During power-up/down (or partial up/down), all I/Os are
tristated, provided VCCA ramps up within a diode drop of VCCI. VCCA and VCCI do not have to be stable.
during power-up/down, and they do not require a specific power-up or power-down sequence in order to
avoid damage to the eX devices. In addition, all outputs can be programmed to have a weak resistor pull-
up or pull-down for output tristate at power-up. After the eX device is plugged into an electrically active
system, the device will not degrade the reliability of or cause damage to the host system. The device's
output pins are driven to a high impedance state until normal chip operating conditions are reached.
Applications, which also applies to the eX devices, for more information on hot swapping.
Power Requirements
Power consumption is extremely low for the eX family due to the low capacitance of the antifuse
interconnects. The antifuse architecture does not require active circuitry to hold a charge (as do SRAM or
EPROM), making it the lowest-power FPGA architecture available today.
Low Power Mode
The eX family has been designed with a Low Power Mode. This feature, activated with setting the special
LP pin to HIGH for a period longer than 800 ns, is particularly useful for battery-operated systems where
battery life is a primary concern. In this mode, the core of the device is turned off and the device
consumes minimal power with low standby current. In addition, all input buffers are turned off, and all
outputs and bidirectional buffers are tristated when the device enters this mode. Since the core of the
device is turned off, the states of the registers are lost. The device must be re-initialized when returning
to normal operating mode. I/Os can be driven during LP mode. For details, refer to the Design for Low Devices. Clock pins should be driven either HIGH or LOW and should not float; otherwise, they will draw
current and burn power. The device must be re-initialized when exiting LP mode.
Table 1-2 I/O Features
Function
Description
Input
Buffer
Threshold
Selection
5.0V TTL
3.3V LVTTL
2.5V LVCMOS2
Nominal Output Drive
5.0V TTL/CMOS
3.3V LVTTL
2.5V LVCMOS 2
Output Buffer
“Hot-Swap” Capability
I/O on an unpowered device does not sink current
Can be used for “cold sparing”
Selectable on an individual I/O basis
Individually selectable low-slew option
Power-Up
Individually selectable pull ups and pull downs during power-up (default is to power up in
tristate)
Enables deterministic power-up of device
VCCA and VCCI can be powered in any order